Method of producing zinc oxide



Patented Feb. 13, 1923.

@FFHQE.

EARL P. STEVENSON, OF CAMBRIDGE, MASSACHUSETTS, ASSIGNOR T ARTHUR D.

LITTLE, INC., 01 CAMBRIDGE, MASSACHUSETTS, CORPORATION 015 MASSA- CHUSETTS,

METHOD OF PRODUCING ZINC OXIDE.

1i 0 Drawing.

lo tion, such as will enable Others skilled in the art to which it appertains to make and use the same.

- The present invention relatesto a method of treating zinc bearing materials and more particularly to a process of producing z nc oxide from such materlals.

The uses of zinc oxide in the practicalarts I are manifold and in all cases it is highly desirable that the oxide shall be pure white in color, although in some instances this is not.

absolutely essential. The color in the zinc oxide is normally dueto the presence of contaminating traces of the oxide of other metals as'copper, iron, cadmium, etc., although this discoloration may occur in a pure zinc oxide due to the physical treatment to which it may have been subjected. At the present time there are relatively fewsources from which a zinc'oxide of this this country being limited substantially to certain relatively small bodies of carbonate ore.

The object of the present invention is to provide an efiicient and relatively inexpensive method applicable to various forms of zinc bearing materials which will produce zinc oxide of a pure white color and free from contaminating traces of other metals. With this object in View, a feature of the invention contemplates the utilization ofthe basic sulphate of zinc produced as set rfioi' th in a co-pending ap lication of Stevenson, Serial No. 326,283 fi ed September 25., 1919.

This compound of zinc is first digested with a soluble alkali and the resulting precipitateafter separation from the solution is then calcined at a low heat to produce zinc oxide. The product resulting from thislmethod is pure White in color and comparesfavorably with the highest grade of zinc oxide prov duced by any other known method.

The process by which this superior grade character may be obtained, the sources in Application filed November 11, 1919. Serial No. 337,319.

of zinc oxide is produced may consist of the following steps beginning with the initials; treatment of the zinc bearing material and ending with the commercial product. In case the zinc bearing ore is in the form of a sulphide, the zinc may be converted into an oxide form by roasting, and in the same manner it the ore contains zinc in the form of a carbonate, it may be converted into an oxide form by-calcining. A ,mixture .in

which zincoccurs either'as an oxide, carbonate, or hydroxide 'isxthen treated in a 5' closed chamber Wlth' a solution of ammo-f ninm sulphate having preferably about 30% concentration. and ,ata temperature of approximatly100 centigradeh In this connectionit may be stated, however, that the 7 concentration of the solution may vary from 20% to 40% and the temperature from 100 to 150 Centigrade and still obtain the desired form of precipitate. The solution of ammonium sulphate is then cooled to precipitate out a basic sulphate of zinc having a well defined crystalline structure of platelike form. This precipitate, after being filtered oil from the solution, is first washed and then dried at a temperature sufficiently high to completely decompose Whatever ammonium salts it may be contaminated With.. The precipitate is then digested with a soluble alkali, such for example as sodium carbonate. The alkali decomposes the sulphate of zinc, converting it into a mixture of zinc hydroxide and zinc carbonate. This precipitate of hydroxide. and carbonate is next separated from the solution by filtering and is then washed, dried and finally calcined at a low; heat to produce commercial zinc oxide. The fact that the precipitate is in the form of a carbonate renders it unnecsary to employ an extremely high temperaure for its conversion into an oxide, it havmg been found that a temperature of about 350 centigrade is suflicient for this purpose. In order to produce the oxide from other zinc compounds by calcining, it is necessary to subject the compound to a temper- 1 0 ature of about 1000 centigrade which turns the zinc compound a bright yellow in color and frequently causes the resultant oxide to assume a cream color rather than a pure white. The advantage ofdealing with zinc in the form of a carbonate resides in the fact that the low temperature employed in the calcining operation is insufiicient to permanently discolor the resultant oxide.

It will be observed that the above described method of producing zinc oxide embodies the utilization of the basic sulphate of zinc having certain characteristic features hereinbefore described. It may be added that this basic sulphate of zinc so called differs from the usual or normal zinc sulphate in that it contains a substantially higher percentage of zinc than the normal sulphate.

In case the zinc bearing material initially treated contains impurities in certain forms, they may be removed before precipitation of the basic sulphate of zinc in the following manner: The presence of iron in the form of ferric oxide, which condition may always be obtained by a proper preliminary roasting, is not objectionable, as this ferric oxide will not dissolve in ammonium'sulphate solution. In a like manner, manganlc oxide is not soluble in the solution of ammonium sulphate. The manganic oxide is more difficult to obtain, however, through roasting and it may be advisable and necessary under certain conditions to add a suitable oxidizing agent to the hot solution of ammonium sulphate in order to convert any manganousoxide which may be present into the corresponding manganic oxide or manganese "dioxide. Ammonium persulphate is apparently preferable for this purpose although other oxidizing agents such asc-hlorine, calcium oxychloride (chloride of lime) and.

" permanganates may also be used. If any sulphate.

cadmium or copper be present in the zinc bearing material initially treated, the will be dissolved by the ammonium su phate along with the zinc but may be eliminated from the hot extraction liquor by treatment with metallic zinc which precipitates the cadmium, copper, and also silver according to well known metallurgical principles. Compounds of lead sulphate and lead oxide, in both of which conditions lead may occur, are insoluble in the solution of ammonium It will be seen from the foregoin tion that the present formation of a zinc oxide free from discoloration and which may be employedas a descripprocess results in the' pigment either in paints or enamels, as a maoxide which consists inf treating a'zincsbeam ing'material with a hot concentrated 'so 'lu-' tion of ammonium sulphate, cooling the solution to precipitate out'a basic sulphate ofv zinc digesting the basic sulphate with Ia soluble alkali and calcining the precipitate oxide. a I 7 2. A Iprocess for the production of Z1n0 oxide w 10h consists in treating zinc bearing material with a hot concentrated solution'of formed in'the soluble alkali'to produce zinc.

ammonium sulphate, cooling the solution to precipitate out a basic sulphate of zinc, di-

- gesting the basic sulphate with a solution of an alkaline carbonate and 'finall calcining the precipitate of zinc car nate-zinc hydroxide formed to produce zincoxide.

3. A process for/the production o fij g'inc oxide which consists in treatingzinc hearing material with a hot concentrated solution of ammonium sulphate, treating the solution with re-agents while still hot to remove other metals therefrom, cooling the solution to precipitate out a basic sulphate of zinc, digesting the basic sulphate with a solution of a carbonate of an alkali metal and finally calcining the zinc carbonate-zinc hydroxide thus formed to produce zinc oxide.

4:. A process for the production of zinc oxide which consists in treating zinc bearing material with a hot concentrated solution of ammonium sulphate, treating the solution with re-agents while still .hot to remove,

other metals, coolin the solution to precipitate out a basic sulphate of zinc, washing, drying the basic su phate at-atemperature high enou h to decompose the ammonium salt with w ich it is contaminated, digesting the basic sulphate with a solution of sodium carbonate and finally calcining the zinc carbonate-zinc h droxide thus formed to pro-' ducezincox e.

. ier r. sTEvaNso 

